Electric welding system



Oct. 30, 1951 1. w. cox ET AL 2,573,094

ELECTRIC WELDING SYSTEM Filed March 9, 1946 63 1 L If THYRATRON l5 CONDUCTING- C B Patented Oct. 30, 1951 ELECTRIC WELDING SYSTEM Irvin W. Cox, West Allis, and Jerome B. Welch, Milwaukee, Wis., assignors to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Application March 9, 1946, Serial No. 653,269

7 Claims.

This invention relates to the control of current impulses and while not limited thereto is particularly adapted to the control of supply of welding current to a workpiece which is to be welded.

An object of the invention is to provide means for supplying automatically from a welding transformer a single unidirectional welding current impulse, in response to energization of a pilot circuit.

Another object is to provide means requiring deenergization of said pilot circuit following supply of a current impulse in response to energization of said circuit.

Another object is to provide in a system of the aforementioned type means for demagnetizing of the welding transformer after the impulse has ceased.

Another object is to provide means to prevent sparking at the welding electrodes resulting from initiation of the flow of secondary transformer current, at the instant of contact or separation of the welding electrodes and the work.

Other objects and advantages will hereinafter appear.

The accompanying drawing is illustrative of an embodiment of the invention.

In the drawing, Figure 1 is a diagram of connections of a welding system, While Fig. 2 is a diagram of the voltages and currents obtaining in the system under various conditions.

In the drawing, L and L are the bus bars of an alternating current supply circuit. The circuit supplies power to a welding transforme I0,

.having a primary winding l and a secondary windin Ill". The secondary winding It? is connected to welding electrodes II which are operated in the usual manner to weld parts clamped therebetween. One terminal of the winding [0 is connected to the bus bar L while the second terminal is connected to the cathode l2 of a gaseous tube or ignitron I2. The tube l2 has also an anode I2 which is connected to the bus bar L and an ignition electrode I2 The ignition electrode 12 is connected to the cathode Ill of a gaseous electron tube or thyratron l3, which tube has an anode 13 connected through a resistor M to the bus bar L and additionally has a control electrode l3.

Connected across the terminals of the primary winding of transformer I0 is the primary winding of an auxiliary transformer I5 which is provided with a secondary winding [5 The energy for operating the ignition circuit of the system is supplied by a transformer I 6 which has a primary winding Hi and three center tapped secondary windings l6", I8 and [6 The secondary winding W has its outside taps connected to the anodes li and ll of a full wave rectifying tube H, which has a filamentary cathode Il The center tap of the winding 16* is connected to an auxiliary bus bar E8. The cathode l'l is connected to the two outside terminals of the transformer winding Hi to be supplied with heating energy therefrom, while the center tap of winding 16 is connected to an auxil iary bus bar I 9 which is positive with respect to bus bar I8. Connected between the bus bars l8 and I9 and in series with each other are three voltage dividing resistors 26, 2! and 22. A resistor 23 is connected in series with a resistor 24 between the common terminal of the resistors 20 and 2| and the grid i3 of tube [3 to normally impress the potential of this common terminal upon the control electrode l3 A smoothing condenser 25 may be connected between the control electrode l3 and the cathode I3="-. The voltage which is impressed upon the grid I3 is controlled b a gaseous tube or thyratron 26 having a cathode 26 and anode 26', a control electrode 26 and a shielding electrode 26 The cathode 26 is connected to the common terminal of the resistors 2| and 22. The control electrode 25 is connected to one terminal of the transformer winding l5, while the other terminal of said transformer winding is connected to the bus bar I 8. The anode 26 may be connected through a normally open contact 2i of an electromagnetic switch 21 to the common terminal of resistors 23 and 24. The switch 21 has an energizing winding 21 and a normally closed contact 21. The winding 27 is connected in series with a pushbutton or other type of normally open switch 28 across the lines L and L To control the moment of ignition of the tube [3, which in turn controls the ignition of the tube l2, the system is provided with a phase shifting network comprising a condenser 29 which is connected in series with a variable resistor 36 across the outer terminals of the transformer winding 6 while the center terminal [6 of said winding is connected to the bus bar 9. The normally closed contacts 27 are connected across the resistor 30 so as to short circuit the same when the switch 21 is deenergized.

The cathodes l3 and 26 may be heated in any conventional manner from any suitable source and as this forms no part of the invention provision for heating the same has been omitted from the drawing.

A resistor 3| of relatively high ohmic value is connected in shunt with the winding Ill of transformer HI and a reactance or resistance 32 is connected in shunt with the tube l2.

The operation of the system is as follows: With the pushbutton switch 28 open, the electromagnetic switch 21 is deenergized. Therefore, the main discharge path of the tube 26 is interrupted and the tube is non-conducting. With the lines L 4 and L energized no current can flow through the tube I2 unless a voltage of sufficient magnitude to initiate an ignition current is supplied to the ignition electrode l2 during some moment of the positive half cycle of the alternating voltage impressed upon said tube. This occurs if the tube I3 is rendered conducting during the same positive half cycle. The tube I3 is rendered conducting during the positive half cycle when the potential of the grid [3 is less'negative than the critical grid voltage of said tube. It will be observed that normally the grid 13 has impressed thereon a negative unidirectional potential with respect to the cathode H substantially equal to the voltage drop through the resistor 20. This voltage is indicated by the horizontal line B in the diagram of Fig. 2, while the sinusoidal line A represents the voltage between the cathode and the anode when the tube is non-conducting. It will be observed that the voltage B is more negative than the critical ignition voltage indicated by the curve C.

There is also impressed upon said grid [3 an alternating potential from the winding Hi which winding is so connected that said potential leads by 180 degrees the voltage between the main electrodes. This latter potential is superposed upon the voltage B resulting in the voltage B. It will be noted that during the positive half cycle of the anode voltage the resultant voltage of the grid l3 is never less negative than the critical voltage C and therefore the tubes [3 and 12 remain non-conducting. If now the pushbutton switch 23 is depressed, the relay 2! is energized, thereby opening the contacts 21 and closing the contacts 21 Opening the contacts 21 inserts a variable part of the resistor 30 into the condenser-resistor network comprisin the condenser 29 and resistor 39, which causes in a well known manner a retardation of the potential of the grid 13 with respect to the cathode I3 so that the grid voltage is shifted as shown by the curve D. It will be observed that now the grid voltage intersects the curve C for the critical voltage near the beginning of the positive half cycle of the cathode voltage A so that the tube I3 becomes conducting during the major part of the positive half cycle. As the tube l3 becomes conducting it passes ignition current from line L through the tube G3 to the ignition electrode l2, the cathode 2 through the transformer winding IE to line L This ignition current causes the breakdown of the tube I2 and the latter becomes conducting, thereby passing current from line L through the tube l2, through the primary winding lii of the transformer ill to line L. This in turn induces a current in the secondary winding ,lil which passes between the welding electrodes H and the latter perform the welding work.

The resistor 39 of the phase shaft network is preferably adjusted so that the voltage curve D intersects the ignition voltage curve C substantially at the beginning of the positive half cycle of the voltage A between the main electrodes, so as to insure the flow of welding current during substantially the entire positive half cycle.

The closure of the contacts 2'l completes the circuit for the main electrodes of the tube 26 so that a continuous voltage is impressed thereon which is equal to the voltage drop through the resistor 2|. The flow of current through the tube 12 also energizes the primary winding l5 of the transformer 15, which induces a voltage in the secondary winding [5 to impress upon the control electrode 26 a voltage which renders the tube 26 conducting. The flow of current through the tube 26 continues as long as the contact 21 are closed and produces a voltage drop in the resistor 23 which depresses the voltage of the grid 13 as indicated by the curve E to prevent restarting of conduction of the tube 13 during the next succeeding positive half cycle. The tube l3 thus prevents re-ignition of the tube 12 and only a single impulse of current is sent through the transformer winding w regardless of how long the pushbutton switch 28 remains closed.

In order to provide for another impulse of current through the welding transformer it is necessary to release the pushbutton 28 thereby reclosing the contacts 21 and opening the contacts 21. Opening of the contacts 2? interrupts the current flowing through the tube 26, so that the potential of the ignition electrode l3 returns again from that shown by curve E to that shown by curve B whereupon the equipment is ready for another impulse.

It should be pointed out that the current which normally flows through the resistor 32 in shunt with the tube i2 is too small in view of the bias provided by the potential drop across resistor 22 to induce a voltage in the transformer windings I l and l5 sufiicient to render the tube 26 conducting. However, the current which flows through resistor 32, winding W to line L provides an alternating demagnetizing flux in said winding to reduce the residual magnetism in transformer l0 due to the high magnetization from a previous operation.

This demagnetizing current in turn induces a voltage in the secondary winding lll which is of low value. To avoid any flashing at the welding electrodes H as they come in contact with or leave the work, the secondary current is bypassed through the resistor 3|.

We claim:

1. The combination of an alternating current supply, a welding transformer having a primary and a secondary winding, an ignitron in circuit with said supply and said primary winding, a first and a second thyratron, said first thyratron having its main discharge path connected in circuit with said supply and the ignition electrode of said ignitron to control supply of ignition current to the latter, means to normally impress upon the control electrode of said first thyratron a voltage varying in synchronism with the voltage of said supply which blocks current conduction by said thyratron, manually actuated means operable to modify the voltage impressed upon said control electrode of said first thyratron to render it conducting during a positive half cycle of the supply voltage and to impress a unidirectional voltage upon the main discharge path of said second thyratron, and means responsive to the flow of current in said ignitron to initiate current flow in said second thyratron for neutralizing the effect of said manually actuated means upon said first thyratron pending release and re-actuation of said manually actuated means.

2. The combination of an alternating current supply, a welding transformer having a primary and a secondary winding, an ignitron in circuit with said supply and said primary winding, a first and a second thyratron, said first thyratron having its main discharge path connected in circuit with said supply and the ignition electrode of said ignitron to controlv supply of ignition current to the latter, means to normally impress upon the control electrode of said first thyratron a voltage varying in synchronism with the voltage of said supply which blocks current conduction by said thyratron, manually actuated means operable to modify the voltage impressed upon said control electrode of said first thyratron to render it conducting during a positive half cycle of the supply voltage and to impress a unidirectional voltage upon the main discharge path of said second thyratron, means responsive to the flow of current in said ignitron to initiate current flow in said second thyratron, and means responsive to current flow in said second thyratron to neutralize the effect of said manually actuated means upon said first thyratron, pending release and re-actuation of said manually actuated means.

3. The combination with an alternating current welding transformer having a primary and a secondary winding and a unidirectionally conducting device controllable to supply a half wave of rectified current to said primary winding, of a relatively high impedance connected in parallel with said device to aiford passage of an alternating demagnetizing current of relatively low magnitude through said primary winding while said device is non-conducting.

4. The combination with an alternating current Welding transformer having a primary and a secondary winding and a unidirectionally conducting device controllable to supply a half wave of rectified current to said primary winding, of an impedance connected in parallel with said device, said impedance being proportioned to permit the passage of current through said primary winding to afiord demagnetization of said transformer following the passage of welding current through said device, but to limit the magnitude of said demagnetizing current to a value below that which efiects welding action.

5. In an alternating current welding system, the combination with an alternating current transformer having a primary and a secondary winding, a pair of welding electrodes connected to the latter and a unidirectional conducting device in series with said primary winding and controllable to supply half wave rectified current to said primary winding, of means to supply an alternating demagnetizing current of relatively low magnitude to said primary winding while said device is non-conducting, and a high resistance connected in parallel with said electrodes to afford a discharge path for the current induced in said secondary winding by said demagnetizing current.

6. The combination of an alternating current supply, a welding transformer having a primary and a secondary winding, an ignitron in circuit with said supply and said primary winding, a relatively high impedance in parallel with said ignitron to afford passage through said Winding of an alternating current of relatively low magnitude while said ignitron is non-conducting, a first and a second thyratron, said first thyratron having its main discharge path connected in circuit with said supply and the ignition electrode of said ignitron to control supply of ignition current to the latter, means to normally impress upon a control electrode of said first thyratron a voltage varying in synchronism with the voltage of said supply which blocks current conduction by said thyratron, manually actuated means operable to modify the voltage impressed upon said control electrode of said first thyratron to render it conducting during a positive half cycle of the supply voltage and to impress a unidirectional voltage upon the main discharge path of said second thyratron, and means responsive to the flow of current in said ignitron to initiate current flow in said second thyratron for neutralizing the eifect of said manually actuated means upon said first thyratron pending release and reactuation of said manually actuated means.

7. The combination of an alternating current supply, a welding transformer having a primary and a secondary winding, an ignitron in circuit with said supply and said primary winding, an impedance in parallel with said ignitron which impedance following passage of Welding current through said ignitron permits passage of current through said primary winding for demagnetizing the same and limits the demagnetizing current to a value below that required for welding, a first and a second thyratron, said first thyratron having its main discharge path connected in circuit with said supply and the ignition electrode of said ignitron to control supply of ignition current to the latter, means to normally impress upon the control electrode of said first thyratron a voltage varying in synchronism with the voltage of said supply Which blocks current conduction by said thyratron, manually actuated means operable to modify the voltage impressed upon said control electrode of said first thyratron to render it conducting during a positive half cycle of the supply voltage and to impress a unidirectional voltage upon the main discharge path of said second thyratron, means responsive to the flow of current in said ignitron to initiate current flow in said second thyratron, and means responsive to current flow in said second thyratron to neutralize the effect of said manually actuated means upon said first thyratron, pending release and reactuation of said manually actuated means.

IRVIN W. COX. JEROME B. WELCI-I.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,904,485 Livingston Apr. 18, 1933 1,928,812 Dawson Oct. 3, 1933 2,024,173 Langmuir Dec. 17, 1935 2,066,943 Philpott Jan. 5, 1937 2,089,213 Labadie Aug. 10, 1937 2,120,565 Lord et al June 14, 1938 2,255,652 Dawson et al Sept. 9, 1941 2,294,388 Dawson Sept. 1, 1942 2,295,293 Rogers Sept. 8, 1942 2,340,131 Lord Jan. 25, 1944 2,355,633 Dawson Aug. 15, 1944 2,356,765 Klemperer Aug. 29, 1944 2,362,769 Paratt et a1 Nov. 14, 1944 2,439,938 Lee et al. Apr. 20, 1948 FOREIGN PATENTS Number Country Date 420,100 Great Britain Nov. 26, 1934 423,166 Great Britain Jan. 16, 1935 

